Nuclear magnetic resonant (NMR) is a test procedure which does not involve invasion of the human body. It can be implemented risk free without side effects or cumulative exposure problems. The signals obtained from it can be recorded and subsequently analyzed.
With these advantages in mind, the present apparatus and method set forth a safe breast cancer detection system. This apparatus is particularly capable of detecting tumorous masses in the human breast, a both malignant and benign. A particular advantage of the present apparatus is the fact that it can make relatively quick measurements without bodily invasion, thereby yielding tumor information. It has been discovered that a significant portion of the tissue in the region of the breast (both normal tissue and tumorous tissus) is made up of water. There are differing binding levels for the hydrogen in the water. The tissue of interest provides one response if the tissue is normal. A different response is provided by cancerous tissue. The difference shows up in comparison of signals obtained from adjacent slices or segments interrogated by NMR techniques. In other words, the data from a first slice is subtracted from data obtained from the adjacent second slice to yield a first difference signal. Second and third difference signals are obtained in like fashion. The signals are graphed as a function of breast length to locate the position within the breast of each data point, and to further isolate anomalies in data indicative of tumors.
This apparatus and the method related thereto utilizes NMR interrogation for the express purpose of obtaining data derived from the hydrogen (water) concentration and the spin-lattice or the spin-spin relaxation times of hydrogen, often identified by the constants T.sub.1 and T.sub.2. Through this analysis, the concentration of loosely bound water in the body tissue can be determined. Equally, the concentration of more tightly bound water in the body tissue can be determined.
As a means of placing the equipment in near proximity so that data can be obtained, the present invention contemplates the use of a changing magnetic field. This can be obtained by forming a fixed magnetic field of proper field intensity and moving the magnet toward the patient undergoing testing. One alternative to this is to utilize a fixed magnet and vary the magnetizing current, thereby changing the field intensity and creating a segment of the field of proper field strength. Alternate arrangements utilizing combinations of changing field current or magnet location will enhance the investigation procedure set forth herein.
The changing field enables an isolated portion of the body tissue to be examined. It takes advantage of the relationship obtained from the frequency of the interrogation pulse and magnetic intensity. For a given frequency, there is a single magnetic intensity. If the field is shaped with a gradient, only a portion of the field will define the proper magnetic intensity. This intensity is identified by the symbol H.sub.o. This field intensity is found in a region within the magnetic field, and does not normally encompass the entire magnetic field region. Rather, the field has other values of intensity (radiofrequency magnetic field), identified by the symbol H.sub.1. This magnetic field intensity is neither too weak or too strong but sufficient to cause the transient NMR effect desired. This magnetic field intensity must be of sufficient magnitude to accomplish the necessary NMR response. The magnetic field gradient is used to advantage to thereby limit the portion of body tissue exposed to NMR interrogation. This portion can be described as a thin slice of body tissue. The thickness of the slice can be controlled dependent on the magnetic field gradient. Ideally, the slice is relatively thin, typically even as thin as one millimeter. By changing the relative position of the proper magnetic field intensity H.sub.o, sequential slices of the breast region can then be observed, tested and anomalies identified. Assuming a maximum breast length of perhaps 15 centimeters, this provides about 150 segments of one millimeter thickness. Assuming that there is a measure of overlap between each test interrogation, perhaps as many as 300 data points might be obtained. A short interval is required to obtain each data point because the polarization time for the hydrogen nuclei making up the body tissue is relatively short, and the perturbations arising from each prior pulsed NMR interrogation is relatively short lived.
With the foregoing in view, the present apparatus is summarized as a structure including an examination table having a hole or holes therein to enable a patient undergoing tests to recline on the table, placing one breast or both breasts through openings in the table. This extends the breast and assures that the breast is within the operating range of the NMR test equipment. Multiple test points are obtained. The magnetic field intensity is varied so that the field intensity segments the breast into a number of relatively thin test volumes, each having a relatively thin dimension and each comprising a relatively thin slice. The test apparatus includes a magnetic field controller. This controls the current applied to the electromagnet to thereby define the field. A transmitter forms a pulse at a selected frequency which is applied to a coil. The coil is positioned so that it surrounds the breast, enabling the breast to be inserted into the coil volume for interrogation.
The equipment also includes a NMR receiver connected to the coil. The receiver is output to a circuit measuring the difference between consecutive received signals. This difference is supplied to a recorder which records the different signals as a function of breast length. Breast length is defined as the dimension of the magnetic field area wherein the breast is placed. Inasmuch as multiple data points are obtained, the output of the apparatus is a signal which is a function of length. Anomalies in the difference signal are indicative of a tumor or other mass causing distortion in the data arising from differences in tightly bound and loosely bound water within the body tissue.